In a technical field of a rotational electric machine, it is required to reduce amount of the rare materials which forms a permanent magnet. Generally, the rotator has a ring-shaped permanent magnet. In order to reduce the amount of the permanent magnet, it can be configured that a plurality of permanent magnets are arranged circumferentially. Compared with the ring-shaped permanent, the amount of the permanent magnet can be reduced.
When multiple permanent magnets are arranged circumferentially, it is important to fix each permanent magnet on an iron core properly. For example, JP-2012-249354A describes that a flat surface of the permanent magnet is fixed on a flat surface of the iron core. A protrusion of the iron core is engaged with a groove of the permanent magnet.
However, in JP-2012-249354A, a gap clearance is necessary between the protrusion of the iron core and the permanent magnet to engage them. Thus, when assembling the permanent magnet to the iron core, it is likely that the permanent magnet moves in the groove relative to the iron core.
If the permanent magnet moves, a magnetic-flux-strength maximum position also deviates in a circumferential direction. The deviation of the magnetic-flux-strength maximum position causes an increase of a cogging torque and a torque ripple.
Moreover, when the magnetic-flux-strength maximum position deviates, the d-axis also deviates in performing a dq-transformation. As the result, controllability is deteriorated and a vibration is caused.